I have seen documentation for rest api integration but there is only room creation and listing participant so how can I create whole video calling app using PHP or python as there are no documentation related to this on https://www.twilio.com/docs/video/
Twilio developer evangelist here.
You can create a whole Video calling app using PHP and Twilio Video. The thing is, you need an interface with which to see the Video app too. This can be done in JavaScript, iOS or Android.
You will need PHP (or Python, or any server side language) to generate access tokens so that your users can authenticate with Twilio Video.
To get started I recommend you check out the Twilio SDK starter for PHP. This is a starter application with PHP that shows you how to integrate Video (and Chat and Sync).
Once you understand how the PHP fits in, check out this getting started guide to Twilio Video in JavaScript.
That should get you going. Let me know if there's anything else I can help with.